From: Richard Biener <rguenther@suse.de>
Date: Wed, 29 Jan 2025 12:25:14 +0000 (+0100)
Subject: tree-optimization/114052 - consider infinite sub-loops when lowering iter bound
X-Git-Tag: releases/gcc-14.3.0~470
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c886bd9ab21429a11bea393b5a6e7438a1d924ef;p=thirdparty%2Fgcc.git

tree-optimization/114052 - consider infinite sub-loops when lowering iter bound

When we walk stmts to find always executed stmts with UB in the last
iteration to be able to reduce the iteration count by one we fail
to consider infinite subloops in the last iteration that would make
such stmt not execute.  The following adds this.

	PR tree-optimization/114052
	* tree-ssa-loop-niter.cc (maybe_lower_iteration_bound): Check
	for infinite subloops we might not exit.

	* gcc.dg/pr114052-1.c: New testcase.
---

diff --git a/gcc/testsuite/gcc.dg/pr114052-1.c b/gcc/testsuite/gcc.dg/pr114052-1.c
new file mode 100644
index 00000000000..e971f684414
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr114052-1.c
@@ -0,0 +1,40 @@
+/* { dg-do run } */
+/* { dg-require-effective-target signal } */
+/* { dg-options "-O2" } */
+
+#include <stdint.h>
+#include <unistd.h>
+#include <signal.h>
+#include <stdlib.h>
+
+volatile int y;
+void __attribute__((noipa)) put(int x)
+{
+  if (y)
+    __builtin_printf ("%i\n", x);
+}
+
+void __attribute__((noipa)) f(void)
+{
+  int counter = 0;
+  while (1) {
+      if (counter >= 2) continue;
+      put (counter++);
+  }
+}
+
+void do_exit (int i)
+{
+  exit (0);
+}
+
+int main()
+{
+  struct sigaction s;
+  sigemptyset (&s.sa_mask);
+  s.sa_handler = do_exit;
+  s.sa_flags = 0;
+  sigaction (SIGALRM, &s, NULL);
+  alarm (1);
+  f();
+}
diff --git a/gcc/tree-ssa-loop-niter.cc b/gcc/tree-ssa-loop-niter.cc
index ba4b056e96e..4392bbb7f68 100644
--- a/gcc/tree-ssa-loop-niter.cc
+++ b/gcc/tree-ssa-loop-niter.cc
@@ -4686,7 +4686,14 @@ maybe_lower_iteration_bound (class loop *loop)
           FOR_EACH_EDGE (e, ei, bb->succs)
 	    {
 	      if (loop_exit_edge_p (loop, e)
-		  || e == loop_latch_edge (loop))
+		  || e == loop_latch_edge (loop)
+		  /* When exiting an inner loop, verify it is finite.  */
+		  || (!flow_bb_inside_loop_p (bb->loop_father, e->dest)
+		      && !finite_loop_p (bb->loop_father))
+		  /* When we enter an irreducible region and the entry
+		     does not contain a bounding stmt assume it might be
+		     infinite.  */
+		  || (bb->flags & BB_IRREDUCIBLE_LOOP))
 		{
 		  found_exit = true;
 		  break;